Integrated circuits incorporating high voltage lateral elements include both metal-oxide-semiconductor field-effect transistors (MOSFETs) devices and bipolar junction transistors. A common use of a power MOSFET in an integrated circuit is as an electronic switch. One known high-voltage MOSFET structure for an integrated circuit includes a drain contact connected to the drain end of a channel by a lateral drain extension, which has the same conductively type as the drain contact. High voltage breakdown is achieved by designing the drain extension with an integrated doping (dopant ions per cm2) such that the drain extension totally depletes at high drain voltages, before the point where avalanche breakdown occurs at a pn junction between the drain extension and the MOSFET body.
Along with size of the structure, there are two other key characteristics of a MOSFET when used in an integrated circuit as an electronic switch. The first is its breakdown voltage and the second is its ON resistance. The breakdown voltage is a measure of the MOSFET's ability to withstand a reversed bias voltage when it is in an OFF or open condition. The ON resistance is a measure of the resistance when the MOSFET is in an ON or closed condition. Improving the operation of the MOSFET switch in an integrated circuit suggests a breakdown voltage as high as possible and an ON resistance as low as possible. A perfect switching device has an infinite breakdown voltage and zero ON resistance. Accordingly, it is desired in the art to reduced the ON resistance. One way of reducing the ON resistance of a lateral MOSFET device is to accurately align various regions of the MOSFET to achieve predefined space between the regions. Unfortunately this is difficult to do with existing techniques because mask edges used to form the various regions introduce an uncertainty factor called an alignment tolerance that contributes to the space between the regions.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art there is a need for a method of accurately controlling the distance between various regions in integrated circuits.